Recently, as high definition television receivers or large television receivers spread rapidly, there is an increasing demand for high definition display devices. Liquid crystal displays (LCD) are one of the leading flat panel displays (FPD) along with electro luminescence (EL) displays and plasma display panels (PDP). The liquid crystal displays have advantages of light weight, space-saving, low cost, low energy consumption or the like.
At present, most of the liquid crystal displays used in the high definition television receivers or large television receivers are transmissive liquid crystal displays. The transmissive liquid crystal displays have a configuration in which liquid crystal is held between two glass substrates each having an electrode formed thereon. A liquid crystal molecular orientation in a liquid crystal layer is changed by a voltage applied to the electrodes formed on the inner sides of the substrates. The optical characteristics of the liquid crystal layer are changed based on the change in liquid crystal molecular orientation as described above. Accordingly, from an orientation relationship with a polarizing plate fixed on the substrate, a transmitted light intensity from a backlight is adjusted to display an image.
Although the transmissive liquid crystal displays are broadly divided into a passive type and an active type from the standpoint of a driving method, most of the present transmissive liquid crystal displays are the active type. In the active type liquid crystal displays, a switching element is provided in each pixel, and the operation of each pixel is thereby controlled. A three-terminal thin film transistor (TFT) is often used as the switching element.
An active matrix substrate where active elements such as the thin film transistors are formed over the entire surface is manufactured by repeating processes of photolithography and etching a plurality of times. That is, a gate wiring, a gate insulating film, a semiconductor layer, a source wiring, a drain wiring, an interlayer insulating film, and a pixel electrode are sequentially laminated respectively by the photolithography process, the etching process or the like.
Meanwhile, display characteristics such as high brightness and visibility are required in this type of liquid crystal display. Various efforts have been made to improve a so-called aperture ratio. For example, a technique disclosed in Patent Document 1 is one of the examples. In Patent Document 1, a pixel electrode is provided overlapping a gate wiring or a source wiring that is a light shielding portion, to thereby increase the aperture ratio and improve the display characteristics.    [Patent Document 1] Japanese Patent Laid-Open No. 2007-52040